SUMMARY OF THE INVENTION
The invention relates to a heat exchanger having, on a first and a second side, inlets and outlets, respectively, for a preferably gaseous heat exchanging medium, and having a heat exchanging component made of a high thermal conductive material, such as metal, in which the heat exchanging material has a structure permeable to the heat exchanging medium, and, in which material, channels, positioned side by side and passing from the inlet side to the outlet side, are formed, such that medium flowing in via the inlet channels can flow to the adjacent outlet channels at an angle to the direction of entry into the heat exchanging material. Further, the invention relates to a method of manufacturing such a heat exchanger. Also, the invention comprises applications of such a heat exchanger.
Such a heat exchanger is known from European Patent Publication No. 376,365. In that case, the heat exchanging material in the heat exchanging component is composed of rows of thin wire elements which are virtually triangular in cross-section and project from the base of the triangular shape. All this produces a particularly large heat dissipating surface area, making it possible, notably on account of the special way in which the gaseous heat exchanging medium is compelled to flow, to attain an exceptionally high heat transfer. However, manufacturing the known heat exchanger is not so easy, particularly in the case of larger runs or mass production.
The invention has for its object to provide a heat exchanger of the type mentioned in the opening paragraph with a high coefficient of heat transfer, of which, in principle, large runs can be manufactured simply and efficaciously and for which mass production is readily workable. The heat exchanger according to the invention is characterized firstly in that the heat exchanging component is comprised of a number of lamellae assembled or joined in the form of a permeable package or structure, the lamellae being made of a foil, preferably of copper, of a thickness of 5 to 1000 .mu.m, with the desired pattern of the permeable structure and with inlet and outlet channels being formed in the foil. The at least partially contacting lamellae each extend substantially in a direction transverse to the longitudinal direction of the intermediate inlet and outlet channels.
A particularly favorable embodiment of the heat exchanger is characterized according to the invention in that said permeable structure in each lamella is made of one and the same foil and is formed integral with a base strip to which heat is fed during operation, and that the adjacent base strips of successive lamellae in the package together form a base plate, with the permeable structure in a lamella at the side opposite to the base strip being formed integral with a bearing strip, preferably with the permeable structure in a lamella at the side facing away from the base strip being provided with a vertical top strip formed integral therewith, such that the top strips of successive lamellae form baffles for the medium, the top strips in a lamella preferably being formed integral with the bearing strips. According to the invention, it is of advantage for the base strip and the bearing strip in each lamella to be joined at their ends to connecting strips formed integral therewith.
A preferred embodiment of the heat exchanger is characterized according to the invention in that the permeable structure is formed by a lattice of straight and/or curved lattice bars disposed in the plane of a lamella and having a width, in the plane of the lamella, of 5 to 1000 .mu.m, measured in the direction parallel to the base strip, it being preferred for the permeable structure in a lamella in the direction away from the base strip to have, for instance, a gradually, narrowing width in the plane of the lamella, with successive permeable structures in a lamella virtually connecting where their widths at the base strip are greatest, or being not more than 5 to 1000 .mu.m removed from each other.
Favorable results have been obtained with a heat exchanger characterized according to the invention in that the permeable structure in a lamella is formed by a group of straight and/or curved lattice bars or lattice wires extending toward the base strip in the shape of a fan. The heat exchanger according to the invention is advantageously characterized in that the circumferential or side edges of the permeable structures of successive lamellae constitute permeable side walls of said inlet and outlet channels for the medium. According to the invention, it is possible to attain good medium permeability when the heat exchanger is characterized in that the construction of the lamellae is such that lattice bars at the circumferential edges of the permeable structures in successive lamellae are staggered. An efficacious embodiment of the heat exchanger is characterized according to the invention in that the construction is such that the width of the inlet channels in the heat exchanging medium feed direction decreases, e.g. gradually or stepwise, while the width of the medium outlet channels in the medium discharge direction increases, e.g. gradually or stepwise. Satisfactory thermal conduction from the heat generating source to the heat exchanger is obtained when the heat exchanger according to the invention is characterized in that the adjacent, base plate-forming base strips of successive lamellae are ground flat on the side facing away from the open structures. Proper unity of the heat exchanging component is obtained when the heat exchanger according to the invention is characterized in that the lamellae forming the heat exchanging component are fixedly interconnected to form a package by means of two or more welding zones provided on the outside of the package. The complicated shaping of the lamellae can be effected with great accuracy in a simple and economical manner even in mass manufacturing if, according to the invention, the desired permeable structure pattern, the inlet and outlet channel widths in the medium, and the base strip are formed by an operation selected from the group of etching, more particularly photochemical etching, build-up, and punching.
According to the invention, the heat exchanger can be efficaciously manufactured when the manufacturing method is characterized in that a plurality, say 100 to 10,000, of lamellae having the desired pattern of the permeable structure and the width of the inlet and outlet channels in the medium are stacked one on top of the other in the desired relative arrangement and pressed together in the form of a package, after which the lamellae are interconnected, preferably by welding on the outside of the package, the welded joint being made with, say, a laser beam or an electron beam. According to the invention, it is of advantage for the package of fixedly joined lamellae to be ground flat at the base strip side of the lamellae facing away from the open structures, and for the lamellae having the desired permeable structure pattern, the inlet and outlet channel widths in the medium, the base strip, the bearing strip and, optionally, the top strip to be made of a foil, preferably a metal foil. According to the invention, the lamellae can be formed from foil in an efficacious manner by an operation preferably selected from the group of etching, more particularly photochemical etching, and punching, the advantage of the process being that it comprises forming a plurality of lamellae side by side in a flat strip of foil, after which, according to the invention, the strip of foil containing a plurality of lamellae is conveyed to a place for mounting or stacking, where the lamellae are removed from the strip of foil, e.g. piece by piece, and then interconnected or stacked in the desired relative arrangement.
According to the invention, the heat exchanger of the described type according to the invention can be employed with advantage in a semi-conductor module comprising at least one semi-conductor chip which is directly or indirectly connected to said heat exchanger base plate at the back.
In the aforementioned etching process the excess material is removed from the foil by etching, which may be referred to as a subtractive method. An alternative manufacturing method, which may be called additive, comprises the electrochemical build-up or deposition on a carrier of metal, more particularly copper, in the pattern desired for the lamella, followed by removal of the carrier.
The invention further comprises a device for heating or cooling, such as a Peltier element, or for use in a car, said device being provided with a power source which is selected from an accumulator, solar cells, batteries or other sources of energy not permanently connected to the supply system, and equipped with a heat exchanger of the above-described type according to the invention. Notably the use of the heat exchanger according to the invention in heating or cooling devices of the types mentioned may give substantial savings in weight and space, it being possible to make the lamellae of aluminum, instead of copper, if so desired.
Another type of heat exchanger, more particularly for cooling electronic components, is disclosed in European Patent Publication No. 267,772. In this case, the cooling member is comprised of a plurality of substantially parallel plate-type cooling fins, said plates being approximately in the shape of a right-angled triangle and mounted, with their bottom shortest legs, side by side, on a base element which absorbs the heat of heat-generating electronic components. The cooling fins are so mounted on the base that the hypotenuses of consecutive fins intersect. Between the upper sections of consecutive cooling fins passageways for cooling air are provided. In the embodiment according to FIGS. 7-10 of this European patent publication a plurality of consecutive cooling fins have been folded from a single strip of metal foil.
European Patent Publication No. 278,240 discloses a different type of cooling member for electronic components, which is substantially comprised of a number of spaced apart parallel flat lamellae mounted on a base plate with heat generating elements. Alternatively, the lamellae may be made from a corrugated metal sheet.
French Patent No. 2,401,525 describes a heat exchanger with flat cooling ribs for use in a thermoelectric device on the basis of the Peltier effect.
In European Patent Publication No. 243,710 a semiconductor module is described having a heat exchanger with conventional fins standing up from a flexible sheet of thermally conductive material sufficiently large to cover an array of chips.
European Patent Publication No. 285,779 describes a different type of cooling system for semi-conductor modules. More particularly, the FIG. 4 embodiment shown in this patent publication has a number of rows of parallel spaced plate-type cooling fins with special spacers provided therebetween. The groups of cooling fins are mounted on a base element which absorbs the heat generated by a number of semiconductor chips. Such an apparatus is a comparatively complex one, particularly in view of the special coolant ducts having arched top walls and flat heavy bottom walls.